Background and Goal of Study: Currently there is no effective therapy for neonatal asphyxia once the insult has occurred. This study investigated whether hyperbaric oxygen ameliorated cerebral injury in a rat model of neonatal asphyxia. Materials and Methods: Four groups of 7 day-old Sprague-Dawley rat pups, each group n=5, were anesthetized by intraperitoneal ketamine injection. The right common carotid artery was ligated and the pups were exposed to 8percent oxygen for three hours, a model used extensively to simulate cerebral injury associated with neonatal asphyxia (1). Study animals were then placed in a hyperbaric chamber and received 100percent oxygen at 3 atmospheres absolute pressure for 60 minutes at either 1, 3 or 6 hours following hypoxia. The animals were sacrificed 10 days later, and the brains weighed. Data were analyzed using one-way ANOVA and Student's two-tailed t-test. P less than 0.05 considered significant. APS/NIH guidelines were observed. Results and Discussion: All animals receiving hyperbaric oxygen had significant preservation of brain weight, with the greatest effect seen when the therapy was applied 1 hour following hypoxic injury. Control animals had significantly lower brain weights and the size difference was clearly visible. Group N Brain Weight (g) SEM p, Control 5 0.8950 0.0290, HBO at 1 Hr. 5 1.3770 0.2690 less than 0.05, HBO at 3 Hr. 5 1.2090 0.1250 less than 0.05, HBO at 6 Hr. 5 1.2490 0.0400 less than 0.05 We found that hyperbaric oxygen when applied as late as 6 hours following hypoxic injury significantly preserved brain weight. Further studies are underway to evaluate the biochemical and molecular implications of this therapy and ultimately assess its clinical efficacy in humans. Conclusions: Hyperbaric oxygen applied within 6 hours of hypoxic injury significantly preserves brain weight in a rat model of neonatal asphyxia. References: 1) Sheldon RA, Partridge JC, Ferriero DM. Pediatr Res 1992; 32: 489-93.